Telephone system having reduced sensitivity to RF interference and related methods

ABSTRACT

A telephone to be connected to a wireline having reduced sensitivity to RF interference over a predetermined frequency range from an adjacent mobile wireless communications device may include a transmit amplifier, a receive amplifier, an audio input transducer connected to the transmit amplifier, and an audio output transducer connected to the receive amplifier. The telephone may further include an RF shield(s) surrounding the audio input transducer and the audio output transducer for reducing RF interference over the predetermined frequency range from the adjacent mobile wireless communications device. Moreover, the telephone may also include at least one RF audio input filter element connected to the audio input transducer and at least one RF audio output filter element connected to the audio output transducer, both of which are also for reducing RF interference over the predetermined frequency range from the adjacent mobile wireless communications device.

FIELD OF THE INVENTION

The present invention relates to the field of communications systems,and, more particularly, to telephone systems and related methods.

BACKGROUND OF THE INVENTION

Cellular communications systems continue to grow in popularity and havebecome an integral part of both personal and business communications.Cellular telephones allow users to place and receive voice calls mostanywhere they travel. Moreover, as cellular telephone technology hasincreased, so too has the functionality of cellular devices and thedifferent types of devices available to uses. For example, many cellulardevices now incorporate personal digital assistant (PDA) features suchas calendars, address books, task lists, etc. Moreover, suchmulti-function devices may also allow users to wirelessly send andreceive electronic mail (email) messages and access the Internet via acellular network and/or a wireless local area network (WLAN), forexample.

Accordingly, because of the widespread use and reliance on cellulardevices, many users carry their cellular devices on their person much ofthe day, and place them on their desks at work. Yet, since cellulardevices are frequently communicating with a cellular network even when auser is not participating in a phone call, they are frequently emittingradio frequency (RF) signals. When in close proximity to a land linetelephone, such as a private branch exchange (PBX) phone in a workplace,these RF signals may cause interference which results in an audible buzzor other undesirable sound by the PBX phone.

Certain PBX telephone devices have generally attempted to addressinterference from other sources. By way of example, U.S. Pat. No.6,473,495 to Willer is directed to a home network environmentimplemented in a customer premises having a PBX for outputting analogtelephone signals onto twisted pair wiring arranged in a star topology.This is done by adding a high pass filter in parallel along the twistedpair wiring. The high pass filter enables transmission of network datasignals between the telephone line pairs connected to the PBX withoutinterference of the switching operations by the PBX of analog telephonesignals. The high pass filter may be implemented within the PBX, oradded externally to the PBX system as a retrofit for existing customerpremises.

Despite such attempts to address certain interference problems in PBXtelephone systems, further protection may be required to significantlymitigate the effects of RF interference from a nearby cellular device,for example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a telephone according to theinvention having reduced sensitivity to RF interference from an adjacentmobile wireless communications device.

FIG. 2 is a schematic circuit diagram of the audio input transducer andassociated filter elements of the telephone of FIG. 1.

FIG. 3 is a schematic circuit diagram of the audio output transducer andassociated filter elements of the telephone of FIG. 1.

FIG. 4 is a schematic block diagram of an alternate embodiment of thetelephone of FIG. 1.

FIG. 5 is a schematic circuit diagram of another alternate embodiment ofthe telephone of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present description is made with reference to the accompanyingdrawings, in which preferred embodiments are shown. However, manydifferent embodiments may be used, and thus the description should notbe construed as limited to the embodiments set forth herein. Rather,these embodiments are provided so that this disclosure will be thoroughand complete. Like numbers refer to like elements throughout, and primeand multiple prime notation are used to indicate similar elements inalternate embodiments.

Generally speaking, a telephone to be connected to a wireline isdisclosed herein having reduced sensitivity to RF interference over apredetermined frequency range from an adjacent mobile wirelesscommunications device. The telephone may include a transmit amplifier, areceive amplifier, an audio input transducer connected to the transmitamplifier, and an audio output transducer connected to the receiveamplifier. The telephone may further include at least one RF shieldsurrounding the audio input transducer and the audio output transducerfor reducing RF interference over the predetermined frequency range fromthe adjacent mobile wireless communications device. Moreover, thetelephone may also include at least one RF audio input filter elementconnected to the audio input transducer for reducing RF interferenceover the predetermined frequency range from the adjacent mobile wirelesscommunications device. In addition, at least one RF audio output filterelement may be connected to the audio output transducer for reducing RFinterference over the predetermined frequency range from the adjacentmobile wireless communications device.

By way of example, the at least one RF audio input filter element andthe at least one RF audio output filter element may each include atleast one series connected ferrite bead and at least one parallelconnected capacitor and, more particularly, a plurality of seriesconnected ferrite beads and a plurality of parallel connectedcapacitors. The predetermined frequency range may be from about 30 MHzto 6 GHz, for example. In addition, the telephone may further include ahybrid circuit connected between the transmit and receive amplifies andthe wireline, and a housing carrying the transmit and receiveamplifiers.

Furthermore, the at least one RF shield may include a first RF shieldfor the audio input transducer and a second RF shield for the audiooutput transducer. The telephone may further include an analog todigital converter (ADC) connected to the transmitter amplifier, and adigital to analog converter (DAC) connected to the receiver amplifier.As such, the at least one RF shield may also surround the ADC and theDAC.

A related method aspect is for reducing sensitivity of a telephone, suchas the one described briefly above, to RF interference over apredetermined frequency range from an adjacent mobile wirelesscommunications device. The method may include positioning at least oneRF shield to surround the audio input transducer and the audio outputtransducer for reducing RF interference over the predetermined frequencyrange from the adjacent mobile wireless communications device. Moreover,at least one RF audio input filter element may be connected to the audioinput transducer for reducing RF interference over the predeterminedfrequency range from the adjacent mobile wireless communications device.The method may further include connecting at least one RF audio outputfilter element to the audio output transducer for reducing RFinterference over the predetermined frequency range from the adjacentmobile wireless communications device.

Referring now more particularly to FIG. 1, a telephone 20, such as a PBXtelephone, for example, to be connected to a wireline or PBX system hasreduced sensitivity to RF interference from RF electromagnetic (EM)energy 21 from an adjacent mobile wireless communications device 22. Inparticular, the RF signals transmitted by the mobile wirelesscommunications device 22 are within one or more predetermined frequencyranges or bands, as will be appreciated by those skilled in the art. Byway of example, the mobile wireless communications device 22 may be acellular communications device, a WLAN device, a personal area network(PAN) device, etc. Transmissions from the mobile wireless communicationsdevice 22 can cause interference at the telephone 20 that results inundesirable audible noises, such as buzzing, for example. As will bedescribed further below, the telephone 20 advantageously includes RFfilter elements and an RF shield(s) to reduce the sensitivity of thedevice to such close-proximity RF interference from the EM energy 21emanating from the mobile wireless communications device 22.

The telephone 22 illustratively includes a housing 23, a transmitamplifier 24, a receive amplifier 25, an audio input transducer (e.g., amicrophone) 26 connected to the transmit amplifier, and an audio outputtransducer (e.g., a speaker) 27 connected to the receive amplifier.Moreover, a hybrid circuit 43 selectively connects the transmitamplifier 24 and the receive amplifier 25 to the wireline, as will beappreciated by those skilled in the art.

It should be noted that in the illustrated embodiment the above-notedcomponents are shown within a single housing 23, but in some embodimentsmore than one housing may be used. For example, a base housing may beconnected to the wireline, and a handset housing may be connected to thebase housing via a wired or wireless communications link, as will beappreciated by those skilled in the art. As such, different componentsmay be located in different housings in different embodiments, as willalso be appreciated by those skilled in the art. By way of example, asingle housing may be appropriate for a “conference room” style speakerphone for multiple users, and the base/handset version may beappropriate for a personal desktop telephone embodiment. Of course, somephones may have similar components in both the base and the handset,e.g., a desktop phone that includes speakerphone capabilities.

The telephone 20 also illustratively includes one or more RF shields 28surrounding the audio input transducer 26 and the audio outputtransducer 27 for advantageously reducing RF interference over thepredetermined frequency range from the adjacent mobile wirelesscommunications device 22. Moreover, the telephone 20 furtherillustratively includes one or more RF audio input filter elements 30connected to the audio input transducer 26, and one or more RF audiooutput filter elements 31 connected to the audio output transducer 27,both of which are for reducing RF interference over the predeterminedfrequency range from the adjacent mobile wireless communications device22. By way of example, the predetermined frequency range may be fromabout 30 MHz to 6 GHz, for a cellular communications device, forexample.

Turning more particularly to FIG. 2, an exemplary implementation of RFaudio input filter elements illustratively includes a first ferrite beadFB_M3 connected in series between the microphone 26 and a highdifferential voltage connection Vin_P, and a second ferrite bead FB_M4connected in series between the microphone 26 and a low differentialvoltage connection Vin_N. Moreover, capacitors C_Mdc1 and C_Mdc2 areconnected in parallel with the microphone 26 and are respectivelypositioned on the microphone side and the differential input connectionside of the ferrite beads FB_M3, FB_M4 as shown in FIG. 2. By way ofexample, for filtering RF interference in the above-noted frequencyrange, the ferrite beads FB_M3 and FB_M4 may be Murata BLM15HD182SN1 andBLM15HD182SN1 filters, and the capacitors C_Mdc1 and C_Mdc2 may be 33pF, for example, respectively. Of course, other values and filterelement components/configurations may be used in different embodimentsdepending upon the particular frequency range to be filtered, the typesof circuit components used in the telephone 20, etc., as will beappreciated by those skilled in the art.

Referring additionally to FIG. 3, the RF audio output filter elementsmay include a first ferrite bead FB_E1 connected in series between thespeaker 27 and voltage output connection Vout, and a second ferrite beadFB_E2 connected in series between the speaker 27 and a voltage reference(i.e., ground). Moreover, capacitors C_Pdc1 and C_Pdc2 are connected inparallel with the speaker 27 and are respectively positioned on thespeaker side and the voltage output connection Vout side of the ferritebeads FB_E1, FB_E2 as shown in FIG. 3. Again, for filtering RFinterference in the above-noted frequency range, exemplary componentsfor the ferrite beads FB_E1 and FB_E2 may be a Murata BLM15HD182SN1 andBLM15HD182SN1, and the capacitors C_Pdc1 and C_Pdc2 may be 33 pF, forexample. Again, other values and filter elements/configurations may beused in different embodiments depending upon the particular frequencyrange to be filtered, the types of circuit components used in thetelephone 20, etc., as will be appreciated by those skilled in the art.Moreover, other values and filter element configurations may be used indifferent embodiments as noted above.

Turning additionally to FIG. 4, another exemplary embodiment of a basicPBX telephone 20′ is now described. The telephone 20′ illustrativelyincludes a transmit attenuator 40′ connected between the transmitamplifier 24′ and a hybrid circuit 43′. Moreover, in the illustratedembodiment a pair of receive amplifiers 25 a′, 25 b′ are connectedbetween the hybrid circuit 43′ and the RF output filter element(s) 31′.A receive attenuator 42′ is connected between the output of the receiveamplifier 25 a′ and the input of the receive amplifier 25 b′, and anattenuator controller 44′ is connected to the transmit attenuator 40′and the receive attenuator. In addition, a first logarithmic detector45′ is connected between the output of the transmit amplifier 24′ andthe attenuator controller 44′, and a second logarithmic detector 46′ isconnected between the output of the receive amplifier 25 a′ and theattenuator controller, as shown. The functions and operation of thevarious attenuation components and hybrid circuit 43′ will be readilyappreciated by those skilled in the art and therefore require no furtherdiscussion herein.

Referring now additionally to FIG. 5, another alternate embodiment of amore advanced PBX telephone 20″ is described. In this embodiment, muchof the phone circuitry is implemented with a digital signal processor50″ and associated digital microcontroller 51″ connected thereto. Aswill be appreciated by those skilled in the art, the digital signalprocessor 50″ and associated digital microcontroller 51″ implementvarious telephone circuit functions, such as those described above andothers, based upon software modules designed for the given phoneimplementation. The digital microcontroller 51″ has a plurality ofinput/outputs (I/Os) including volume up and down, privacy, connect,echo suppression, auto answering, setup/operate, auto initialize, andvolume limit, as will be appreciated by those skilled in the art. Thedigital microcontroller 51″ may also optionally include a remote controlinterface with connect switch, privacy switch, volume up/down switch,and connect LED and privacy LED inputs, as will also be appreciated bythose skilled in the art. The digital signal processor 50″ alsoillustratively has transmit and receive signal and limit I/Os as shown.

The transmit signal path illustratively includes a transmit amplifier 24a″ connected to the microphone and associated RF filter, which may be asshown in FIG. 2. A transmit level adjuster 52″ is downstream from thetransmit amplifier 24 a″, a limiter 53″ is downstream from the transmitlevel adjuster, and an analog-to-digital (A/D) converter (ADC) 54″ isconnected between the limiter and the digital signal processor 50″.Additional RF filter elements may also be connected in this signal path,including an ferrite bead FB_M connected between the transmit leveladjuster and a first input of a mix out amplifier 55″, a capacitor C_dc1connected in parallel with the input of the limiter 53″, and a capacitorC_dc2 connected in parallel with the output of the limiter, as shown.Furthermore, a digital-to-analog (D/A) converter (DAC) 56″ is connecteddownstream from the digital signal processor 50″, and another transmitamplifier 24 b″ is downstream from the DAC. The output of the transmitamplifier 24 b″ is connected to the hybrid circuit 43″, which in turnprovides switching to the phone line. A separate telephone line may alsobe included for plugging in peripheral telephone devices (e.g., modems,etc.) to the telephone 20″, as will be appreciated by those skilled inthe art.

The receive signal path illustratively includes a receive amplifier 25a″ downstream from the hybrid circuit 43″, and an ADC 57″ connectedbetween the audio input amplifier 25 a″ and the digital signal processor50′. Moreover, a DAC 58″ and a receive level adjuster 59″ are connectedbetween the digital signal processor 50″ and a transmit amplifier 25″,which is in turn connected to a loudspeaker and associated RF filter,such as those shown in FIG. 3. It should be noted that in theillustrated embodiment, the transmit level adjuster 52″, limiter 53″,ADC 54″, DAC 58″, receive level adjuster 59″, mix out amplifier 55″, anda mix out level adjuster 60″ are advantageously included within the RFshield 28″ to provide still further reduction of RF interference fromthe adjacent wireless communications device 22, as will be appreciatedby those skilled in the art.

The telephone may further include a main bus input from a modular audioprocessor interface and associated switch 61″ connected to a secondinput of the mix out amplifier 60″. The input of the audio outputamplifier 25 b″ is also connected to the input of the mix out amplifier60″, as is the output of a log detector circuit 65″. The log detectorcircuit 65″ is further connected to variable threshold and fixedthreshold references from the modular audio processor interface. Acomparator 66″ has a first input connected to the variable thresholdinput of the log detector 65″, and a second input connected to a voltagereference VREF as shown. The comparator 66″ provides priority and nomsignals for the modular audio processor interface, as will beappreciated by those skilled in the art.

A related method aspect is for reducing sensitivity of the telephone 20to RF interference over a predetermined frequency range from the mobilewireless communications device 22. The method may include positioning atleast one RF shield 28 to surround the audio input transducer 26 and theaudio output transducer 27 for reducing RF interference over thepredetermined frequency range from the adjacent mobile wirelesscommunications device 22. Moreover, at least one RF audio input filterelement 30 may be connected to the audio input transducer 26 forreducing RF interference over the predetermined frequency range from theadjacent mobile wireless communications device 22. The method mayfurther include connecting at least one RF audio output filter element31 to the audio output transducer 27 for reducing RF interference overthe predetermined frequency range from the adjacent mobile wirelesscommunications device 22. Additional method aspects will be appreciatedby those skilled in the art from the foregoing description and thereforerequire no further discussion herein.

Many modifications and other embodiments will come to the mind of oneskilled in the art having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it isunderstood that various modifications and embodiments are intended to beincluded within the scope of the appended claims.

1. A telephone to be connected to a wireline and having reducedsensitivity to RF interference over a predetermined frequency range froman adjacent mobile wireless communications device comprising: a transmitamplifier; a receive amplifier; an audio input transducer connected tosaid transmit amplifier; an audio output transducer connected to saidreceive amplifier; at least one RF shield surrounding said audio inputtransducer and said audio output transducer for reducing RF interferenceover the predetermined frequency range from the adjacent mobile wirelesscommunications device; at least one RF audio input filter elementconnected to said audio input transducer for reducing RF interferenceover the predetermined frequency range from the adjacent mobile wirelesscommunications device; and at least one RF audio output filter elementconnected to said audio output transducer for reducing RF interferenceover the predetermined frequency range from the adjacent mobile wirelesscommunications device.
 2. The telephone of claim 1 wherein said at leastone RF audio input filter element comprises at least one seriesconnected ferrite bead and at least one parallel connected capacitor. 3.The telephone of claim 1 wherein said at least one RF audio input filterelement comprises a plurality of series connected ferrite beads and aplurality of parallel connected capacitors.
 4. The telephone of claim 1wherein said at least one RF audio output filter element comprises atleast one series connected ferrite bead and at least one parallelconnected capacitor.
 5. The telephone of claim 1 wherein said at leastone RF audio output filter element comprises a plurality of seriesconnected ferrite beads and a plurality of parallel connectedcapacitors.
 6. The telephone of claim 1 wherein said at least one RFshield comprises a first RF shield for said audio input transducer and asecond RF shield for said audio output transducer.
 7. The telephone ofclaim 1 wherein the predetermined frequency range is from about 30 MHzto 6 GHz.
 8. The telephone of claim 1 further comprising a hybridcircuit connected between said transmit and receive amplifies and thewireline.
 9. The telephone of claim 1 further comprising: an analog todigital converter (ADC) connected to said transmitter amplifier; and adigital to analog converter (DAC) connected to said receiver amplifier.10. The telephone of claim 9 wherein said at least one RF shield alsosurrounds said ADC and said DAC.
 11. The telephone of claim 1 furthercomprising a housing carrying said transmit and receive amplifiers. 12.A telephone to be connected to a wireline and having reduced sensitivityto RF interference over a predetermined frequency range from an adjacentmobile wireless communications device comprising: a housing; a transmitamplifier carried by said housing; a receive amplifier carried by saidhousing; a hybrid circuit connected between said transmit and receiveamplifies and the wireline; an audio input transducer connected to saidtransmit amplifier; an audio output transducer connected to said receiveamplifier; at least one RF shield surrounding said audio inputtransducer and said audio output transducer for reducing RF interferenceover the predetermined frequency range from the adjacent mobile wirelesscommunications device; at least one RF audio input filter elementconnected to said audio input transducer for reducing RF interferenceover the predetermined frequency range from the adjacent mobile wirelesscommunications device; and at least one RF audio output filter elementconnected to said audio output transducer for reducing RF interferenceover the predetermined frequency range from the adjacent mobile wirelesscommunications device.
 13. The telephone of claim 12 wherein said atleast one RF audio input filter element comprises at least one seriesconnected ferrite bead and at least one parallel connected capacitor.14. The telephone of claim 12 wherein said at least one RF audio outputfilter element comprises at least one series connected ferrite bead andat least one parallel connected capacitor.
 15. The telephone of claim 12wherein said at least one RF shield comprises a first RF shield for saidaudio input transducer and a second RF shield for said audio outputtransducer.
 16. The telephone of claim 12 wherein the predeterminedfrequency range is from about 30 MHz to 6 GHz.
 17. A method for reducingsensitivity of a telephone to be connected to a wireline to RFinterference over a predetermined frequency range from an adjacentmobile wireless communications device, the telephone comprising atransmit amplifier, a receive amplifier, an audio input transducerconnected to the transmit amplifier, and an audio output transducerconnected to the receive amplifier, the method comprising: positioningat least one RF shield to surround the audio input transducer and theaudio output transducer for reducing RF interference over thepredetermined frequency range from the adjacent mobile wirelesscommunications device; connecting at least one RF audio input filterelement to the audio input transducer for reducing RF interference overthe predetermined frequency range from the adjacent mobile wirelesscommunications device; and connecting at least one RF audio outputfilter element to the audio output transducer for reducing RFinterference over the predetermined frequency range from the adjacentmobile wireless communications device.
 18. The method of claim 17wherein the at least one RF audio input filter element comprises atleast one series connected ferrite bead and at least one parallelconnected capacitor.
 19. The method of claim 17 wherein the at least oneRF audio output filter element comprises at least one series connectedferrite bead and at least one parallel connected capacitor.
 20. Themethod of claim 17 wherein positioning the at least one RF shieldcomprises positioning a first RF shield to surround the audio inputtransducer and a second RF shield to surround the audio outputtransducer.
 21. The method of claim 17 wherein the predeterminedfrequency range is from about 30 MHz to 6 GHz.
 22. The method of claim17 wherein the telephone further comprises an analog to digitalconverter (ADC) connected to the transmitter amplifier and a digital toanalog converter (DAC) connected to the receiver amplifier; and whereinpositioning the at least one RF shield comprises positioning the atleast one RF shield to also surround the ADC and the DAC.